THIS AVALANCHE ADVISORY EXPIRED ON January 8, 2017 @ 6:47 am
Avalanche Advisory published on January 7, 2017 @ 6:47 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The Avalanche Danger is Moderate on upper elevation slopes today. Small wind slabs exist throughout upper elevation terrain. Watch for wind sculpted/textured areas and firmer pockets of older wind slab or wind board near ridge tops and wind exposed slopes.  Expect additional loading today and tonight as South winds increase accompanying an incoming storm. The Avalanche Danger will be increasing over the next 24 hours with rising temperatures, gusty winds and the potential for significant precipitation in the upper elevations.

How to read the advisory


  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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  • Likelihood ?
    Certain
    Very Likely
    Likely
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  • Size ?
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This week, the upper elevations have been dominated by light to moderate mostly Northerly winds which were able to move the 5 inches of light density snow around easily, these winds created soft new wind slabs on multiple aspects.  In addition, you can still find the affects of the wind from the weekend and the end of last week. Most of the wind slab problems are going to be found on the northerly aspects where new slabs have been formed on top of older wind slabs. Watch for sculpted or stiff wind board on the windward aspects and rippled, chalky or hollow feeling/sounding pillows and drifts on steep leeward aspects. You should also be aware that some of the older wind slabs may be found well below the ridgelines on leeward terrain.

In addition, these areas are going to require careful evaluation as the new snow begins to camouflage these older slabs over the next 24 hours.  Areas with stiff wind board are going to be shedding snow as well as the new snow starts to accumulate.  Practice safe travel protocols, and expose only one person at a time in wind loaded avalanche terrain. Pay attention to changing conditions over the next few days, the snowpack is going to start developing an attitude as we add additional snow and weight.

recent observations

We toured through some of the most alpine wind effected terrain in the Lake Fork Drainage yesterday and confirmed all of our own forecasts with mostly stable snow on all but a few isolated areas.  Wind slabs and wind affected snow was the dominant feature but for the most part unaffected by our travels.  We did find several pockets of sensitive wind slab on steep E facing terrain and as we were looking at some of the obviously wind affected NE terrain. Shear tests and ski cuts showed thin (less than 2 inch)wind slabs on much of the upper elevation terrain with pockets of deeper slabs pushing into the 6-8 inch range.  

We saw no evidence of recent avalanches other than the small wind slabs that we were intentionally triggering. Cornice growth has been relatively small with the light density snow that we have received so far this winter and the snowpack and coverage is still incredibly variable.  

The most concerning things we observed yesterday were shallow rocky areas mostly on shaded aspects with a very unconsolidated, faceted snowpack all the way to the ground.  Due to the extremely cold temperatures that we have seen this isn't surprising but it will be a concern this week as we add new and wind blown snow and additional weight to these areas.  In addition, ridgetops and exposed terrain have built up a stout and slick wind board that will not allow the incoming new snow to bond to them.  As we add new and wind deposited snow to the existing wind slabs and other problem areas, the scale is going to begin to tip in the favor of bigger avalanches.  The storms coming in this week will be the biggest and most significant storm cycle of the season and our snowpack is going to demand your respect as it changes.

Sastrugi and  wind spines and drifts in the photos below on East and West Facing aspects of Sawtooth Peak.

weather

The National Weather Service has issued a winter storm warning beginning later today and ending tomorrow night.  Forecasts and precipitation models are somewhat conflicted as to how much snow we are going to see but the red flags will be waving with increasing temperatures overnight tonight, S winds rising into the the 30+ range and an as yet undetermined amount of new snow falling.  In addition, the 7 day forecast shows several storms lined up and continuing to bring significant snowfall through next week.  The map below shows the 7 day precipitation forecast in inches of water.  Depending on the temperatures, a good formula is 1 inch of water equals roughly 10 inches of snow.  Local variations will be found, especially over the next 36 hours with NW and W facing slopes picking up additional snowfall.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: Cloudy, then snow after noon. Snow Snow
Temperatures: 16 deg. F. 13 and rising deg. F. 30 deg. F.
Wind direction: S/SE SE E/SE
Wind speed: 7 3-7 3-8
Expected snowfall: 1 in. 1-3 in. less than 1 in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: Snow after 11 Snow Snow
Temperatures: 20 deg. F. 18 and rising deg. F. 31 deg. F.
Wind direction: S S S
Wind speed: 17-22 15-23 gusting to 32 increasing in the am 19-24 in the pm
Expected snowfall: 1-3 in. 2-4 in. 2-4 in.
Disclaimer

This avalanche advisory is provided through a partnership between the Payette National Forest and the Payette Avalanche Center. This advisory covers the West Central Mountains between Hard Butte on the north and Council Mountain on the south. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.